(a) Field of the Invention
This invention relates to an improved apparatus and method for the determination of the nitrogen content of nitrogen-containing matter; more especially the invention is concerned with a method and apparatus for the preparation and measurement of ultra micro amounts of nitrogen gas produced by the combustion of particulate matter in an oxygen environment.
(B) Description of Prior Art
Conventional determinations of nitrogen isotope ratios have been performed in several ways. The most common method has been to do Kjeldahl digestions of the substance being analysed. When properly executed the nitrogen is converted to ammonium sulfate and it is then distilled into a weak acid, an aliquot of which is subsequently back titrated so that the quantity of nitrogen can be calculated. The remaining dissolved ammonium salt is concentrated by evaporation and is then reacted in vacuo with alkaline hypobromite, the product being nitrogen gas. The nitrogen next passes through a liquid nitrogen trap before entering a mass spectrometer for isotope ratio analysis. The same sample preparation procedure has been extensively used for emission spectrometric analysis of isotope ratios.
The Dumas procedure has also been widely used for sample preparation. It is particularly useful because the sample is converted directly from particulate material to nitrogen gas. Unfortunately the manual methods are rather slow and tedious. An automated Dumas method has been developed, however, and it has been successfully connected to a mass spectrometer to enable rapid mass ratio analysis. The disadvantages are that initial costs are high, several qualified personnel are needed to operate the apparati, and the quantity of nitrogen produced is not concurrently measured.
The Dumas procedure has also been applied to emission spectrometers and has been shown to be successful with extremely small amounts of ammonium chloride. However, sample preparation is long and tedious.